1. Field of the Invention
The present invention relates to a computer system, and deals more particularly with a method, system, and computer program product for providing security within a computer network while enabling fine-grained access control for packets traveling through the network.
2. Description of the Related Art
Cryptography is a security mechanism for protecting information from unintended disclosure by transforming the information into a form that is unreadable to humans, and unreadable to machines that are not specially adapted to reversing the transformation back to the original information content. The cryptographic transformation can be performed on data that is to be transmitted electronically, such as an electronic mail message or an electronic document requested by a user of the Internet, and is equally useful for data that is to be securely stored, such as the account records for customers of a bank or credit company.
The transformation process performed on the original data is referred to as “encryption”. The process of reversing the transformation, to restore the original data, is referred to as “decryption”. The terms “encipher” and “decipher” are also used to describe these processes, respectively. A mechanism that can both encipher and decipher is referred to as a “cipher”.
Use of a “key” during the encryption and decryption processes helps make the cipher more difficult to break. A key is a randomly-generated number factored into operation of the encryption to make the result dependent on the key. The value used for the key in effect “personalizes” the algorithm, so that the same algorithm used on the same input data produces a different output for each different key value. When the value of this key is unknown to unauthorized persons, they will not be able to duplicate or to reverse the encryption.
One of the oldest and most common security systems today is what is known as a “private key” or “symmetric” security system. Private key systems involve two users, both of whom have a shared secret (or private) key for encrypting and decrypting information passed between them over a network. Before communications can occur, the two users must communicate in some secure manner to agree on this private key to ensure the key is known only to the two users. An example of a cipher used for private key security is the Data Encryption Algorithm (“DEA”). This algorithm was developed by scientists of the International Business Machines Corporation (“IBM”), and formed the basis of a United States federal standard known as the Data Encryption Standard (“DES”). Private key systems have a number of drawbacks in an open network environment such as the Internet, however, where users will conduct all communications over the open network environment and do not need or want the added overhead and expense of a separate secure means of exchanging key information before secure network communications occur.
To address the limitations of private key systems, security systems known as “public key”, or “asymmetric”, systems evolved. In a public key system, a user has a key pair that consists of a private key and a public key, both keys being used to encrypt and decrypt messages. The private key is never to be divulged or used by anyone but the owner. The public key, on the other hand, is available to anyone who needs to use it. As an example of using the key pair for encrypting a message, the originator of a message encrypts the message using the receiver's public key. The receiver then decrypts the message with his private key. The algorithm and the public key used to encrypt a message can be exposed without compromising the security of the encrypted message, as only the holder of the associated private key will be able to successfully decrypt the message. A key pair can also be used to authenticate, or establish the identity of, a message originator. To use a key pair for authentication, the message originator digitally signs the message (or a digest thereof) using his own private key. The receiver decrypts the digital signature using the sender's public key. A common means of publishing a public key to be used for a particular receiver is in an X.509 certificate, also known as a “digital identity”.
Public key encryption is generally computationally expensive, having numerous exponentiation operations. It also requires much longer key material than a symmetric key algorithm to provide equivalent security. Hence it is used sparingly, preferably only for cryptographic operations that need its unique properties. Symmetric key encryption is more widely used for bulk data encryption/decryption, because it demands less of the CPU, using primarily repeated shift, rotate, exclusive OR, and table lookup operations.
Public and symmetric key encryption methods are often combined. One example of their combination is the Internet Key Exchange (IKE) protocol of the IP Security Protocol (commonly referred to as “IPSec”). IKE is defined in the Internet Engineering Task Force (IETF) document RFC 2409, “The Internet Key Exchange (IKE)”, dated November 1998. IPSec is defined in RFC 2401, “Security Architecture for the Internet Protocol”, also dated November 1998.
IPSec provides security services for traffic at the network layer, or IP (Internet Protocol) layer, of a communications network through use of both cryptographic and protocol security mechanisms. IPSec is designed for protecting data in transit across a non-secure network. IPSec makes no distinctions between public networks such as the Internet and private networks such as a corporate intranet, and can be deployed on either type of network. IPSec may operate at either a host (i.e. an endpoint) or at an intermediate security gateway (including routers and firewalls that provide the functionality of IPSec). The security services available in IPSec include data confidentiality (i.e. encryption), data integrity, data origin authentication, and access control. IPSec may be used to protect packets between two hosts, between a host and a security gateway, or between two security gateways.
A tunneling mode is defined in IPSec, wherein the IP content within a packet is protected according to a selected set of security services. Security associations are created for transmitting packets, where a security association (“SA”) is a logical 1-directional connection defined for purposes of specifying and enforcing the security services to be used. A security association may be created between two hosts, between two security gateways, or between a host and a security gateway. The SA reflects the security services that have been negotiated for the underlying path. For example, if encryption and authentication are required for some communications between particular entities, but only encryption (and not authentication) is required for other communications between these entities, then two separate security associations will be created. The set of security services applicable to an SA are also referred to as a “security policy”.
Tunneled packets in IPSec have an outer IP header whose source and destination addresses identify the endpoints of the tunnel, and an inner IP header whose source and destination addresses identify the originator and recipient of the packet. When IPSec is used in “tunnel” mode, the complete inner packet, which is comprised of both the inner header and the payload, is protected as the packet travels through the tunnel. However, the outer header remains in clear text form as the packet travels through the tunnel. The protection applied to the complete inner packet can be encryption alone, authentication alone, or both encryption and authentication, as specified by the relevant security association negotiated between the tunnel endpoints.
IKE may be used to securely negotiate security associations between the two endpoints of an IPSec tunnel, and to exchange authenticated material from which each endpoint can derive the symmetric keys that will be used for protecting data transmitted on that tunnel. The IKE message exchange comprises two phases. In the first phase, a negotiation is performed, and a secure authenticated control channel (an IKE SA) is established using negotiated attributes (including an encryption algorithm, hashing algorithm, and authentication method). In the second phase, an SA is negotiated on behalf of a security service such as IPSec to establish a secure “traffic” channel for exchanging packets between a pair of communicating end systems.
The steps in a typical phase 1 are: (1) offer and acceptance of the attributes of the IKE SA, which will protect the subsequent IKE negotiation messages; (2) an unauthenticated Diffie-Hellman exchange of keying material that will subsequently be used to derive symmetric encryption and authentication keys for protecting both the IKE messages (i.e. the control flows) and user traffic; and (3) a mutual authentication step that allows each party to authenticate itself to the other using strong cryptographic techniques (thereby ensuring the authenticity of the Diffie-Hellman keying exchange). The phase 2 exchange is then performed to negotiate the IPSec SA, which will be used subsequently to protect user traffic. Furthermore, the packets of the user traffic will be tightly bound to the authenticated identities of the two entities that completed the successful IKE phase 1 negotiation.
However, the prior art does not teach techniques for providing access control that is based on the identities of the communicating entities. IPSec provides an authentication technique, as stated above, but this technique is limited in function and results in access controls that are typically coarse-grained in nature. Application of the authentication process begins with determining an applicable security policy. One or more security policies can be defined in IPSec, and stored in a security policy database (SPD). Incoming packets are then compared to the stored security policy information. If a match is found (i.e. the policy to be applied to the packet can be determined), then the attributes of an SA associated with that policy are used to locate a suitable existing SA or to create a new SA having the required attributes. In this manner, the policy also determines whether the packet will be further processed by IPSec (such as performing encryption and/or authentication on the packet content), or whether the packet is to be forwarded without further IPSec processing, or simply discarded. The IPSec standard states that an administrative interface must be provided to enable specification of the attributes of traffic that will use a particular SA, including the source and destination addresses of data packets. Because of the burden that will be placed on an administrator if detailed information is to be provided (which would enable a finer-grained access control), an SA will tend to have relatively non-specific information (including use of wildcards or address ranges for the source and destination address information), thereby providing coarse-grained access control. That is, a security policy may specify that all packets from IP addresses in the range of 1.2.3.4 to 1.2.3.255 are to use an SA that provides encryption using a particular encryption algorithm. It would be preferable to provide much finer access control granularity, based on (for example) the identity of users of the communicating entities, without placing a burden on an administrator to state massive amounts of detailed information and without adding complex access control processing logic to an IPSec implementation.
U.S. Pat. No. 6,076,168, entitled “Simplified Method of Configuring Internet Protocol Security Tunnels”, teaches a technique for configuring and maintaining security tunnels and packet filters that steer user traffic into or out of those tunnels. However, this patent does not teach a technique for making access control decisions at a fine level of granularity without overburdening a secure transport mechanism. U.S. Pat. No. 5,940,591, entitled “Apparatus and Method for Providing Network Security”, uses logic that is positioned in the upper layers of a communication stack for providing improved network security, and does not allow participation of the end systems in the process. U.S. Pat. No. 6,052,788, entitled “Firewall Providing Enhanced Network Security and User Transparency”, deals with the use of the Domain Name Service (DNS) and application gateways in a firewall. The methods taught therein are address-based, and do not address user identification nor cryptographic authentication. U.S. Pat. No. 5,835,726, entitled “System for Securing the Flow of and Selectively Modifying Packets in a Computer Network”, teaches techniques for inspecting packets but does not discuss ascertaining the identity of the data originator, nor making access control decisions with a fine level of granularity.
Accordingly, what is needed is an improved technique for securely making access control decisions without overburdening system administrators and without adding to the complexity of existing security services such as IPSec.